The present invention relates to a device for lifting prefabricated components, particularly made of concrete, or the like.
Specifically provided devices are conventionally used to allow lifting of prefabricated concrete components and can be grouped substantially into three categories.
A first category of devices is substantially constituted by elements which are embedded in the concrete component during its manufacture and protrude from a perimetric side of the component so that they can be engaged by lifting equipment, such as cranes.
The element that is embedded in the component and protrudes from it in order to be engaged is generally substantially constituted by an iron rod which is shaped like a ring, hook, eyelet or stirrup or by a plate, so that it can be easily engaged directly by the hook of the lifting crane.
Devices that belong to this first category are now obsolete and are almost no longer in use, since the presence of an element that protrudes from the volume of the concrete component is undesirable both for aesthetic reasons and for functional reasons, since it hinders the installation of the component and it must very often be removed.
A second category of devices is constituted by anchoring elements which are plate-shaped or nail-shaped or otherwise shaped and do not protrude from the profile of the component because they are embedded proximate to a perimetric side of the component, providing around them, on said side of the component, a suitable cavity in order to allow their engagement by means of lifting shackles which are connected to the crane.
In practice, these devices that belong to the second category are composed of three basic elements: an anchoring element to be embedded in the component; a throwaway or reusable mold to produce the cavity around the portion of the anchoring element that must be engaged; and a shackle for engaging the anchoring element which is embedded in the component.
Devices that belong to this second category, while solving the problems of the devices of the first category described above, since they do not produce protrusions from the profile of the component, entail problems mainly during the casting of the component, since it is necessary to use the mold to form the cavity around the portion of the anchoring element that is meant to be engaged by the shackle.
Another problem that can be observed in devices of this second category is the fact that the need to have a cavity of suitable size around the element embedded in the concrete component allows use of this device only in rather thick concrete components.
A third category of lifting devices is constituted by anchoring elements which are embedded in the body of the component proximate to one of its perimetric sides and which instead of requiring the provision of a specifically-executed cavity to allow the engagement of the anchoring element by the lifting equipment, have a seat in which a second element is detachably engaged; said second element is meant to protrude from the perimetric side of the component in order to be engaged by the lifting equipment.
In devices that belong to this category, the anchoring element is constituted by a threaded bush which is embedded in the concrete component during its casting, proximate to a perimetric side of the component, so that the opening for accessing said threaded cavity is directed outward.
A threaded pin, meant to protrude from the profile of the concrete component, is then coupled by screwing in said threaded cavity and engaged by the lifting equipment.
Devices that belong to this category considerably simplify the execution of the component, since they do not require use of special molds in order to form a cavity in the concrete component; however, they entail some problems.
In particular, the threaded coupling of the element meant to be engaged by the lifting equipment with the threaded cavity of the bush embedded in the concrete component is not capable of offering adequate assurances of safety, since correct execution of the threaded coupling is entrusted to the operator.
Moreover, since components are usually handled in an environment which is rich in dust and sand, dirt may seep into the threaded cavity, making it difficult to provide correct coupling to the threaded pin, which is meant to be engaged by the lifting equipment.
Furthermore, owing to the fact that the threaded pin is used several times to handle several components, wear of said part is noted; after repeated screwing and unscrewing operations, said wear makes it difficult to couple said pin to the threaded cavities of the anchoring elements embedded in the concrete components.
The gradual increase of the wear of the threaded pin also significantly reduces the degree of safety of the coupling, since said wear can be the primary cause of an accidental release of the component when it is lifted.
Moreover, the coupling of the threaded pin to the bush embedded in the concrete component is relatively slow and troublesome to perform.
Another problem is the fact that the threaded bush has strength problems when the lifting of the component also includes a step for overturning the component, with shearing stresses that concentrate on the threaded bush.